DoorDash OA 面试真题解析：Design a Rewards System for Food Reviews

Design a system that allows DoorDash’s consumers to add reviews on ordered food items. Consumers will earn rewards ($) based on the quality of the review.

Just for reference, rewards are paid on a monthly basis. An example of rules can be:

Upvotes | Rewards
50    | $0.5
100   | $1
1000  | $10

Up to $50 a month and max accumulated of $500.

这道 DoorDash 面试题本质上是在设计一个“按月结算的评论奖励系统”：用户在订餐后可以提交评价，系统根据评价质量（例如点赞数 / 上票数）发放奖励，并且奖励规则可能是分档的，还要受每月上限和累计上限约束。解题时通常要先澄清奖励计算方式，再把规则抽象成可配置的阈值表，便于后续扩展；实现上可以用哈希表或数据库记录用户月度奖励、累计奖励和每条评论的质量指标，计算时按规则匹配对应档位并做封顶处理。若继续深入设计，还需要考虑幂等性、重复提交、月度结算任务、并发更新以及大规模用户下的存储与查询性能。